Many mobile devices enter a low-power or ‘sleep’ mode when a user is not actively utilizing functions of the device. However, even if a user is not engaging with the device, the mobile device cannot perform its duties correctly while remaining constantly in a low-power mode, as it is necessary to monitor incoming signals from a network provider.
Such signals are typically scheduled to arrive at predetermined time intervals as set by network providers, e.g., between 0.5 seconds and 5 seconds. These signals are sometimes referred to as ‘paging signals’ and the data associated therewith are encoded as ‘paging blocks’. If a mobile device is in a low power mode, it needs to “wake up” or enter an active mode, in time to handle a paging signal. Examples of these scenarios are illustrated in scenarios (i), (ii), and (iii) of FIG. 4.
FIG. 4 shows paging signals that a given mobile device is required to periodically receive and process. These signals are periodically transmitted by the network provider, typically wirelessly, for a short burst of just a few microseconds. The mobile device would typically have a baseband processor for processing these signals, and the processor must be in a suitable state for receiving and processing these signals at the time such a signal reaches the mobile device.
Scenario (i) of FIG. 4 shows the regular intervals at which a mobile device can expect to receive incoming signals, and also illustrates the low-power and active modes of the baseband processor.
As shown in scenario (i), if the baseband processor remains fully active even when other features of the mobile device are in a low-power mode, then this will ensure that the paging signal is successfully received and decoded at each of the times when the paging signal is expected. However, it will be appreciated that the microsecond time duration of the incoming signal relative to the seconds between these signals being received constitutes a long idle period where the processor is consuming power but not being utilized.
In between paging signals/activities, it is therefore preferable for the processor to enter a low-power mode (often referred to as ‘sleep mode’) in order to save power. However, due to the fact that the state of the system needs to be restored after being in the low-power/sleep mode, there is an issue of latency that needs to be addressed. This latency time required to restore the state of the system is referred to as ‘restore time’.
It can be difficult to accurately identify a restore time for a given mobile device, not least because, depending on current state of the device, it may take a different duration to come out of the low-power mode to the active mode.
As is illustrated in scenario (ii) of FIG. 4, if the baseband processor is not in a suitable state for processing the paging signal when the paging signal arrives, then this can cause loss of data, e.g., text messages or phone calls.
Alternatively, as shown in Figure (iii), the baseband processor may be moved to the active mode early to ensure reception of the signals, but this results in wasted power.